JP2003041330A - Method for melting titanium ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To melt titanium ingot with high productivity and superior in quality and characteristics. SOLUTION: (1) The method for melting the titanium ingot comprises cooling a smelted ingot in a furnace, discharging it outside the furnace when the surface temperature reaches 300-700 deg.C, cooling it with water until the surface temperature of the above ingot reaches 100-200 deg.C, and then drying the surface. (2) The above method for melting the titanium ingot comprising multistage melting, preferably, cools the smelted ingot with water, dries the surface, and then remelts it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting a titanium ingot containing sponge titanium obtained by the Kroll method as a main raw material. For example, in manufacturing an ingot by a consumable electrode melting method represented by vacuum arc melting. The present invention relates to a method for melting a titanium ingot which shortens the time required for cooling the ingot and can improve the production efficiency even in the case of multi-step melting, and which has excellent quality characteristics.

[0002]

2. Description of the Related Art The Kroll process to which chlorination is applied is generally adopted for industrial production of titanium, which is a refractory metal. Furthermore, in order to avoid contamination from refractory during melting, when manufacturing ingots, which are processing materials for manufacturing plates, rods, tubes, forgings, etc., from titanium sponge obtained by the Kroll method. Melting is performed in a vacuum or in an inert atmosphere by using a mold in which the outside is forcibly cooled with water by using an arc, an electron beam, and plasma as a heat source.

Conventionally, titanium ingot melting methods have been consumable electrode type vacuum arc melting method (VAR), plasma beam melting method (PBR), and electron beam melting method (EB).
R) and electroslag melting method (ESR), the consumable electrode type vacuum arc melting method is widely adopted for melting titanium ingots on an industrial production scale.

Titanium sponge, which is a raw material for melting titanium ingot, is sponge-like crushed particles, which are pressed to form briquettes. At that time, alloying elements and return scrap are uniformly mixed, These briquettes are assembled by bead welding to make a consumable electrode.

FIG. 1 is a diagram for explaining an outline of the whole process including a consumable electrode type vacuum arc melting furnace. As shown in FIG. 1, titanium sponge 1, which is the main raw material for consumable electrodes, is usually compression molded by a compression press 8 to mold a compact 2. The compacted compact 2 is welded by the bead welder 9 to form the consumable electrode 3, and the consumable electrode 3 is melted in the consumable electrode type arc melting furnace 10 to melt the ingot 7.

In the consumable electrode type arc melting furnace, a consumable electrode made of a raw material to be melted is hung from the outside in a water-cooled copper mold in a furnace in a vacuum or an inert gas atmosphere to form an electrode. Arc is generated between the lower end of the electrode and the bottom of the mold by a direct current with negative and positive mold, and the arc is stabilized between the pool of molten metal dropped from the electrode melted by the heat of the arc and the electrode. Let The electrodes are sequentially melted from the bottom, and the pool of melt is solidified from below to form an ingot.

FIG. 2 is a diagram showing the construction of a concrete consumable electrode type vacuum arc melting furnace. As shown in FIG. 2, the consumable electrode 3 is fixed to the stub 13 by welding, and is continuously lowered as the stinger rod 12 is lowered as the melting progresses. In the water-cooled copper mold 11, the consumable electrode 3 melts due to the generation of the arc 4, forms molten titanium 5, and is cooled to form solidified titanium 6. Cooling water is circulated inside the water-cooled copper mold 1 as indicated by an arrow in the figure.

Usually, in the consumable electrode type vacuum arc melting method,
In order to homogenize the composition and reduce surface defects and internal defects, the first melting is followed by the second melting, the third melting and the melting in multiple stages. In order to perform such multi-stage melting, welding with the stub for the next stage of melting is required, so the upper and lower ends of the molten ingot are machined on the end face with a lathe and the stub is welded. There is a need to. Therefore, it is necessary to cool the ingot to the extent that lathe processing and stub welding are possible before repeating melting.

As cooling of the melted ingot, immediately after the melting is completed, until the surface temperature at which oxidation of the ingot does not pose a problem is performed in a melting furnace in a vacuum or a non-oxidizing atmosphere such as Ar gas. A method of cooling and then releasing to the atmosphere and cooling to a surface temperature at which handling is possible has been adopted. However, in this method, it takes a long time for the surface temperature to decrease, and thus there is a problem that the production efficiency is significantly decreased.

[0010]

As described above, in order to carry out multi-step melting, the melted ingot is cooled to a surface temperature at which it can be handled by combining in-furnace cooling and atmospheric cooling. If this is the case, it will take a long time to cool, and the production efficiency will drop significantly. Traditionally,
Cool the ingot in the melting furnace and lower the surface temperature to a predetermined temperature (700 ° C or less) where oxidation does not matter,
It was taken out of the furnace and air-cooled with a blower. But,
The air cooling method requires a long time for cooling,
An additional cooling space had to be installed in the factory, and there was an environmental problem that dust was scattered in the factory.

On the other hand, in order to reduce the cooling time of the melted ingot, it is conceived that the ingot is water-cooled. However, by water cooling, water remains on the surface of the ingot, and the ingot is melted before remelting. It is necessary to prolong the evacuation time in the inside, increase surface defects in the remelted ingot, and increase oxygen concentration are observed. That is, although the cooling time can be shortened by water cooling of the ingot, unless the water cooling conditions are properly selected, the efficiency of the melting operation and the quality improvement will be hindered.

The present invention has been made in view of the problems that occur in the conventional consumable electrode type melting method. When cooling a melted ingot, a combination of cooling inside the furnace and water cooling outside the furnace is used. The objective of the present invention is to provide a method for melting titanium ingots, which not only optimizes water cooling conditions but also adds water rinsing action to the surface of the ingot to shorten the cooling time, improve production efficiency, and further improve quality characteristics. I am trying.

[0013]

In order to solve the above-mentioned problems, the present inventor investigated the various phenomena associated with water cooling by subjecting the ingot after the primary melting to water cooling. surely,
Although the cooling time of the ingot can be shortened by water cooling, the oxygen concentration increased after the secondary melting compared with the conventional air cooling ingot. The increase in oxygen concentration due to such water cooling is due to the fact that magnesium chloride (MgCl ₂ ) remaining on the surface of the ingot after the primary dissolution absorbs water, and that the cooling water remains on the unevenness of the surface.

Therefore, when the ingot is cooled with water, the surface temperature of the ingot is continuously or intermittently measured with a radiation thermometer or a contact thermometer, and the water cooling end temperature (the temperature at which the supply of cooling water to the ingot is ended). The test which changes is carried out. As a result, when the water cooling end temperature was 100 ° C. or higher, no increase in oxygen concentration was observed in the secondary dissolution. Furthermore, it was also clarified that the oxygen concentration in the secondary melting can be reduced as compared with the ingot cooled by air cooling.

If water cooling is stopped when the surface temperature of the ingot is 100 ° C. or higher, the heat retained by the ingot will remove most of the water remaining in the convex and concave portions of the surface and the water taken in by the hygroscopic effect of MgCl _2. Since it can be evaporated, the increase in water due to water cooling is negligible.

[0016] Moreover, when water-cooling the ingot, the cooling water also acts to remove wash away MgCl ₂ remaining on the surface, MgCl ₂ amount remaining on the surface after the water cooling termination,
Less than that of an air-cooled ingot surface. Further, when the MgCl ₂ remaining on the surface is washed off by the cooling water over the entire circumference of the ingot, the MgCl _{2 on the} surface of the ingot is effectively removed, and the amount becomes significantly smaller than that of the air-cooled ingot surface.

When the air-cooled ingot is secondarily melted,
Oxygen is taken in from the moisture absorbed from the atmosphere during cooling. On the other hand, in the ingot cooled according to the present invention, the amount of MgCl ₂ remaining on the surface is reduced, and the water due to water cooling is also sufficiently removed. It is considerably reduced compared to the ingot.

As described above, when the ingot is water-cooled, the amount of MgCl ₂ remaining on the surface is smaller than that when it is air-cooled. However, when water cooling is performed without controlling the water cooling end temperature, the action of the heat retained in the ingot cannot be utilized, and the residual MgCl ₂ absorbs a large amount of water from the cooling water, resulting in The oxygen concentration in the subsequent dissolution will increase.

For example, after cooling the surface temperature of the ingot to less than 100 ° C., it is possible to remove the water content with a warm air dryer or the like, but in that case, the whole ingot is surrounded by a large size to be dried. A warm air dryer is required,
Along with the increase in equipment cost, a new drying process is required, which poses a problem of increase in man-hours and processing time. In addition to these problems, the surface temperature of the ingot is 10
If the temperature is below 0 ° C, the cooling rate of the ingot will be considerably slower than with water cooling at high temperature, and the cooling time will have to be extended considerably. In the case of drying with warm air, the heat of the ingot cannot be effectively used, and there is also a problem in that it is not preferable in terms of energy efficiency.

In other words, when the ingot is air-cooled, it cannot be ignored that MgCl ₂ absorbs moisture in the air to increase the oxygen concentration of the secondary ingot before the secondary melting, but the water cooling is completed. Temperature is ingot surface temperature 100 ℃
By cooling with water under the above conditions, the amount of MgCl ₂ remaining on the surface can be reduced, and
Since MgCl ₂ is secondarily dissolved in a dried state, it is possible to suppress an increase in oxygen concentration.

FIG. 3 is a diagram for explaining an example of a schematic configuration of the water cooling device of the present invention. In the illustrated water cooling device, the melted titanium ingot 7 is allowed to stand still on the ingot stand 14, and the water cooling shower 16 is uniformly supplied through the water cooling pipes 15 over the entire length of the titanium ingot 7, which results in a large cooling time. Can be shortened.

Further, in another configuration example of the water cooling apparatus of the present invention, the water pressure of the cooling water can be increased and the supply amount can be increased in order to effectively remove MgCl ₂ . In this case, for example, a high-pressure water flow outlet may be provided in the circumferential direction of the ingot, and the outlet may be reciprocated along the longitudinal direction of the ingot. Moreover, even if the ingot shown in FIG. 3 is rotated about the axial direction, the water-cooled shower can be applied to all the side surfaces of the ingot, so that MgCl ₂ can be effectively removed as well.

The present invention has been completed based on the above findings, and has as its gist the following methods (1) and (2) for producing a titanium ingot. (1) A method of melting an ingot by using a consumable electrode containing titanium sponge as a main raw material, in which the melted ingot is cooled in the furnace, and when the surface temperature reaches 300 to 700 ° C, the furnace is heated. When released, the surface temperature of the ingot will rise to 10
It is a method for melting a titanium ingot, which is characterized in that the surface is dried after being water-cooled to 0 to 200 ° C. (2) The method for melting the titanium ingot in (1) above is a multi-step melting method, and it is desirable that the melted ingot be water-cooled, the surface thereof be dried, and then redissolved.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION In the melting method of the present invention, in the water cooling operation of the ingot outside the furnace, the temperature released to the outside of the furnace,
By optimizing the water cooling end temperature and the washing action of cooling water, MgCl ₂ remaining on the surface of the ingot after water cooling is reduced, and the heat of the ingot is used to remove water on the surface of the ingot. It is characterized by evaporating. This makes it possible to shorten the vacuum exhaust time before remelting, reduce the surface defects of the remelting ingot, and suppress the increase in oxygen concentration.

The melting method targeted by the present invention is any of a consumable electrode type vacuum arc melting method (VAR), a plasma beam melting method (PBR), an electron beam melting method (EBR), and an electroslag melting method (ESR). Alternatively, a dissolution method combining these may be used. In any case, the objects and effects of the present invention can be achieved.

The melted ingot is cooled in the furnace, and after the surface temperature reaches 300 to 700 ° C., it is discharged to the outside of the furnace and transferred to water cooling of the ingot. Therefore, in the present invention, it is possible to understand that the discharge temperature outside the reactor and the water cooling start temperature are almost the same temperature. In order to sufficiently obtain the effect of shortening the cooling time, which is one of the objects of the present invention, it is desirable to discharge the ingot to the outside of the door and immediately shift to water cooling of the ingot. If the surface temperature of the ingot at the start is 300 to 700 ° C, the effect of the present invention can be achieved.

The lower limit of the temperature released to the outside of the furnace is set to 300 ° C., because if it is cooled to less than 300 ° C., the cooling time in the melting furnace becomes long and the production efficiency remarkably decreases. Further, the effect of removing MgCl ₂ is promoted by the energy that the cooling water boiled vigorously on the surface of the ingot, so that the release temperature immediately before the start of water cooling needs to be 300 ° C. or higher.

On the other hand, when the temperature discharged to the outside of the furnace exceeds 700 ° C., the surface of the ingot is significantly oxidized with water cooling and the oxygen concentration of the ingot increases. Therefore, from the viewpoint of production efficiency and ingot quality, the temperature released outside the furnace after cooling in the melting furnace is
It is desirable that the temperature be 400 to 500 ° C.

In the water cooling operation of the present invention, the water cooling end temperature must be 100 to 200 ° C. at the surface temperature of the ingot. As mentioned above, the surface temperature of the ingot is 100 ℃
If it is less than the above, there is a concern that equipment cost and work man-hours increase due to the drying process. Furthermore, the heat retained by the ingot cannot be effectively utilized, and moisture remains on the surface of the ingot, so the vacuum evacuation time before remelting must be extended, and the surface defects of the remelting ingot increase.
And an increase in oxygen concentration will occur.

On the other hand, when the surface temperature of the ingot at the end of water cooling exceeds 200 ° C., it becomes difficult to form the end surface of the ingot on a lathe and to handle it during stub welding. Because of this, I can't get to work immediately,
There is no choice but to cool in the air until the surface temperature of the ingot falls below 200 ℃. Especially, the surface temperature of the ingot is 20
At around 0 ° C, the cooling rate of the ingot suddenly slows down, so water cooling is terminated at a surface temperature above 200 ° C, and then it is allowed to cool in the atmosphere until the surface temperature falls below 200 ° C. It is not efficient in terms of shortening.

As described above, in the water cooling operation of the present invention, MgCl 2
_Since it is also intended to effectively remove ₂ ,
It is effective to increase the water pressure of the cooling water and increase the supply amount. Therefore, in the present invention, it is desirable that the water pressure of the cooling water is 0.5 MPa or more and the supply amount of the cooling water is 80 liters / minute or more.

In the melting method of the present invention, the moisture on the surface is evaporated by the heat of the ingot, so natural drying is preferable. To further shorten the drying time, it is desirable to blow dry air to accelerate evaporation. In this case, it is desirable that the structure of the ingot device is covered from the viewpoint of preventing dust in the factory.

The size of the target ingot can be arbitrarily selected, and when the size is large, the amount of water is increased to increase the water cooling rate, and at the same time, the temperature of the surface of the ingot may be properly controlled. The surface temperature may be measured at any position on the surface of the ingot, but it is desirable to provide the surface temperature at the upper end and the lower end of the ingot, and use the average value of these as the surface temperature.

The melting method of the present invention can be applied to pure titanium and titanium alloy having similar specific heat and thermal conductivity.

[0035]

EXAMPLES The effects of the dissolution method of the present invention will be described based on specific examples. As shown in FIG. 1, a compact 2 was produced by a compression press 8 using titanium sponge produced by the Kroll method as a main raw material, and then was welded and integrated by a bead welder 9 to form a cylindrical consumable electrode 3. Was manufactured. The consumable electrode was melted in a consumable electrode type vacuum arc melting furnace to prepare a primary melting ingot having a diameter of 660 mm and a weight of 4800 kg.

The molten ingot is cooled in the furnace,
The surface temperature released outside the furnace was measured by the radiation thermometer at the temperature at the upper end of the ingot. The ingot discharged to the outside of the furnace was cooled at a water pressure of 0.5 MPa and a water amount of 100 liters / minute using the cooling device shown in FIG. 3 while measuring the temperature of the upper end with a thermocouple, and the water cooling end temperature was measured. did. The measured temperatures are shown in Table 1.

The ingot that has been sufficiently dried after cooling with water is
The end face of the ingot was formed by a lathe, and the stub was welded to form an electrode for secondary melting. The obtained electrode is remelted in a consumable electrode type vacuum arc melting furnace, diameter 740 mm, weight 4800 kg
The second molten ingot was melted. The oxygen concentration on the upper end surface of the secondary molten ingot was measured and compared with the oxygen concentration of the raw material sponge to confirm the amount of increase in oxygen concentration. Furthermore, the side of the secondary molten ingot is turned by lathe cutting until there are no porosity defects that can be detected by the penetrant flaw detection method,
The cutting depth was measured. Table 1 shows the measured increase in oxygen concentration and the result of cutting depth.

[0038]

[Table 1]

The invention examples (Nos. 1 to 5) satisfying the conditions of the discharge temperature outside the furnace and the end temperature of water cooling specified in the present invention have a small increase in oxygen concentration and a small cutting depth for defect detection.
Further, the working time from the discharge of the primary melting from the furnace to the vacuum exhaust before the secondary melting was as short as 5 to 8.5 Hr, and a good evaluation could be obtained. On the other hand, in Comparative Examples (Nos. 6 to 11) that do not have the conditions of the out-furnace discharge temperature or the water cooling end temperature specified in the present invention, the oxygen concentration increase amount, the cutting depth for defect detection, or One of the working hours was defective, and good evaluation could not be obtained.

[0040]

According to the method for melting a titanium ingot of the present invention, when the molten ingot is cooled, the cooling inside the furnace and the cooling outside the furnace are combined to optimize the water cooling conditions and at the same time, to cool the water. By adding a water-washing action to the surface of the ingot, it is possible to shorten the cooling time, improve the production efficiency, and dissolve the titanium ingot having excellent quality characteristics.

Specifically, the in-furnace discharge temperature of the ingot and the water cooling end temperature are optimized, and further, by the action of washing the cooling water, MgCl ₂ remaining on the surface of the ingot after water cooling is reduced and the heat retained by the ingot is utilized. By evaporating the water on the surface of the ingot, the vacuum exhaust time before remelting is reduced, the surface defects of the remelting ingot are reduced, and the increase of oxygen concentration is suppressed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an outline of an entire process including a consumable electrode type vacuum arc melting furnace.

FIG. 2 is a diagram showing a concrete configuration of a consumable electrode type vacuum arc melting furnace.

FIG. 3 is a diagram illustrating an example of a schematic configuration of a water cooling device of the present invention.

[Explanation of symbols]

1: sponge titanium, 2: compact, 3: consumable electrode, 4: arc, 5: molten titanium, 6: solidified titanium, 7: ingot, 8: compression press, 9: bead welder, 10: consumable electrode type arc melting Furnace, 11: Water-cooled copper mold, 12: Stinger rod, 13: Stub, 14:
Ingot stand, 15: Water cooling pipe, 16: Water cooling shower

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22D 30/00 B22D 30/00 C22B 9/22 C22B 9/22 // C22B 9/18 9/18 A 9 / 187

Claims (2)

[Claims] 1. A method for melting an ingot by using a consumable electrode containing titanium sponge as a main raw material, wherein the melted ingot is cooled in a furnace and its surface temperature is 300 to 700 ° C.
The method for melting a titanium ingot is characterized in that the titanium ingot is discharged to the outside of the furnace at this stage, water-cooled until the surface temperature of the ingot reaches 100 to 200 ° C., and then the surface is dried. 2. Ingot melting is multi-step melting,
The method for melting a titanium ingot according to claim 1, wherein the melted ingot is water-cooled, the surface is dried, and then the melted ingot is redissolved.